Roster API question

I'm building a Sports (baseball) app and I wish for the user to sign into their Yahoo fantasy baseball accounts (only once ideally) so that the app can retrieve what players are in their lineup whenever called upon to do so (i.e. I want my app to make a call before the start of every MLB game that's scheduled for a particular day).

Can the Yahoo Fantasy Sports API do this and more specifically would I use the Rosters API to do this?

I'm a brand new developer and am not very knowledgeable :(

Would anyone be willing to share with me how I would go about doing this if what I proposed is not the way to go about it?